Mammalian bone tissue is known to contain one or more proteinaceous materials, presumably active during growth and natural bone healing, which can induce a developmental cascade of cellular events resulting in endochondral bone formation. This active factor (or factors) has variously been referred to in the literature as bone morphogenetic or morphogenic protein, bone inductive protein, osteogenic protein, osteogenin, or osteoinductive protein.
The developmental cascade of bone differentiation consists of recruitment and proliferation of mesenchymal cells, differentiation of progenitor cells, calcification of cartilage, vascular invasion, bone formation, remodeling, and finally marrow differentiation (Reddi (1981) Collagen Rel. Res. 1:209-226).
Though the precise mechanisms underlying these phenotypic transformations are unclear, it has been shown that the natural endochondral bone differentiation activity of bone matrix can be dissociatively extracted and reconstituted with inactive residual collagenous matrix to restore full bone induction activity (Sampath and Reddi (1981) Proc. Natl. Acad. Sci. USA 78:7599-7603). This provides an experimental method for assaying protein extracts for their ability to induce endochondral bone in vivo. Several species of mammals produce closely related protein as demonstrated by the ability of cross species implants to induce bone formation (Sampath and Reddi (1983) Proc. Natl. Acad. Sci. USA 80:6591-6595).
The potential utility of these proteins has been recognized widely. It is contemplated that the availability of the protein would revolutionize orthopedic medicine, certain types of plastic surgery, dental and various periodontal and craniofacial reconstructive procedures.
The observed properties of these protein fractions have induced an intense research effort in several laboratories directed to isolating and identifying the pure factor or factors responsible for osteogenic activity. The current state of the art of purification of osteogenic protein from mammalian bone is disclosed by Sampath et al. (1987) Proc. Natl. Acad. Sci. USA 84:7109-7113. Urist et al. (1983) Proc. Soc. Exp. Biol. Med. 173:194-199 disclose a human osteogenic protein fraction which was extracted from demineralized cortical bone by means of a calcium chloride-urea inorganic-organic solvent mixture, and retrieved by differential precipitation in guanidine-hydrochloride and preparative gel electrophoresis. The authors report that the protein fraction has an amino acid composition of an acidic polypeptide and a molecular weight in a range of 17-18 kDa. This material was said to be distinct from a protein called "bone derived growth factor" disclosed by Canalis et al. (1980 Science 210:1021-1023, and by Farley et al. (1982) Biochem 21:3508-3513.
Urist et al. (1984) Proc. Natl. Acad. Sci. USA 81:371-375 disclose a bovine bone morphogenetic protein extract having the properties of an acidic polypeptide and a molecular weight of approximately 18 kDa. The authors reported that the protein was present in a fraction separated by hydroxyapatite chromatography, and that it induced bone formation in mouse hindquarter muscle and bone regeneration in trephine defects in rat and dog skulls. Their method of obtaining the extract from bone results in ill-defined and impure preparations.
European Patent Application Ser. No. 148,155, published Oct. 7, 1985, purports to disclose osteogenic proteins derived from bovine, porcine, and human origin. One of the proteins, designated by the inventors as a P3 protein having a molecular weight of 22-24 kDa, is said to have been purified to an essentially homogeneous state. This material is reported to induce bone formation when implanted into animals.
International Application No. PCT/087/01537, published Jan. 14, 1988 (Int. Pub. No. WO88/00205), discloses an impure fraction from bovine bone which has bone induction qualities. The named applicants also disclose putative "bone inductive factors" produced by recombinant DNA techniques. Four DNA sequences were retrieved from human or bovine genomic or cDNA libraries and expressed in recombinant host cells. While the applicants stated that the expressed proteins may be bone morphogenic proteins, bone induction was not demonstrated. This same group reported subsequently ((1988) Science 242:1528-1534) that three of the four factors induce cartilage formation, and postulate that bone formation activity "is due to a mixture of regulatory molecules" and that "bone formation is most likely controlled . . . by the interaction of these molecules." Again, no bone induction was attributed to the products of expression of the cDNAs. See also Urist et al., EPO 0,212,474 entitled "Bone Morphogenic Agents".
Wang et al. (1988) Proc. Nat. Acad. Sci. USA 85: 9484-9488, disclose the partial purification of a bovine bone morphogenetic protein from guanidine extracts of demineralized bone having cartilage and bone formation activity as a basic protein corresponding to a molecular weight of 30 kDa determined from gel elution. Separation of the 30 kDa fraction yielded proteins of 30, 18 and 16 kDa which, upon separation, were inactive. In view of this result, the authors acknowledged that the exact identity of the active material had not been determined.
Wang et al. (1990) Proc. Nat. Acad. Sci. USA 87: 2220-2224 describe the expression and partial purification of one of the cDNA sequences described in PCT 87/01537. Consistent cartilage and/or bone formation with their protein requires a minimum of 600 ng of 50% pure material.
International Application No. PCT/89/04458 published Apr. 19, 1990 (Int. Pub. No. WO90/003733), describes the purification and analysis of a family of osteogenic factors called "P3 OF 31-34". The protein family contains at least four proteins, which are characterized by peptide fragment sequences. The impure mixture P3 OF 31-34 is assayed for osteogenic activity. The activity of the individual proteins is neither assessed nor discussed.
It also has been found that successful implantation of the osteogenic factors for endochondral bone formation requires association of the proteins with a suitable carrier material capable of maintaining the proteins at an in vivo site of application. The carrier should be biocompatible, in vivo biodegradable and porous enough to allow cell infiltration. The insoluble collagen particles remaining after guanidine extraction and delipidation of pulverized bone generally have been found effective in allogenic implants in some species. However, studies have shown that while osteoinductive proteins are useful cross species, the collagenous bone matrix generally used for inducing endochondral bone formation is species-specific (Sampath and Reddi (1983) Proc. Nat. Acad. Sci. USA 80: 6591-6594). Demineralized, delipidated, extracted xenogenic bone matrix carriers implanted in vivo invariably fail to induce osteogenesis, presumably due to inhibitory or immunogenic components in the bone matrix. Even the use of allogenic bone matrix in osteogenic devices may not be sufficient for osteoinductive bone formation in many species. For example, allogenic, subcutaneous implants of demineralized, delipidated monkey bone matrix is reported not to induce bone formation in the monkey. (Asperberg et al. (1988) J. Bone Joint Surg. (Br) 70-B: 625-627).
U.S. Pat. No. 4,563,350, issued Jan. 7, 1986, discloses the use of trypsinized bovine bone matrix as a xenogenic matrix to effect osteogenic activity when implanted with extracted, partially purified bone-inducing protein preparations. Bone formation is said to require the presence of at least 5%, and preferably at least 10%, non-fibrillar collagen. The named inventors claim that removal of telopeptides which are responsible in part for the immunogenicity of collagen preparations is more suitable for xenogenic implants.
European Patent Application Ser. No. 309,241, published Mar. 29, 1989, discloses a device for inducing endochondral bone formation comprising an osteogenic protein preparation, and a matrix carrier comprising 60-98% of either mineral component or bone collagen powder and 2-40% atelopeptide hypoimmunogenic collagen.
Deatherage et al. (1987) Collagen Rel. Res. 7: 2225-2231, purport to disclose an apparently xenogenic implantable device comprising a bovine bone matrix extract that has been minimally purified by a one-step ion exchange column and reconstituted, highly purified human Type-I placental collagen.
U.S. Pat. No. 3,394,370, issued Jul. 7, 1983, describes a matrix of reconstituted collagen purportedly useful in xenogenic implants. The collagen fibers are treated enzymatically to remove potentially immunogenic telopeptides (also the primary source of interfibril crosslinks) and are dissolved to remove associated noncollagen components. The matrix is formulated by dispersing the reconstituted collagen in acetic acid to form a disordered matrix of elementary collagen molecules that is then mixed with osteogenic factor and lyophilized to form a "semi-rigid foam or sponge" that is preferably crosslinked. The formulated matrix is not tested in vivo.
U.S. Pat. No. 4,172,128, issued Oct. 23, 1979, describes a method for degrading and regenerating bone-like material of reduced immunogenicity, said to be useful cross-species. Demineralized bone particles are treated with a swelling agent to dissolve any associated mucopolysaccharides (glycosaminoglycans) and the collagen fibers subsequently dissolved to form a homogenous colloidal solution. A gel of reconstituted fibers then can be formed using physiologically inert mucopolysaccharides and an electrolyte to aid in fibril formation.
It is an object of this invention to provide osteogenic devices comprising matrices containing dispersed osteogenic protein, purified from naturally-sourced material or produced from recombinant DNA, and capable of bone induction in allogenic and xenogenic implants. Another object is to provide novel polypeptide chains useful as subunits of dimeric osteogenic proteins, as well as DNA sequences encoding these polypeptide chains and methods for their production using recombinant DNA techniques. Still another object is to provide recombinant osteogenic proteins expressed from procaryotic or eucaryotic cells, preferably mammalian cells, and capable of inducing endochondral bone formation in mammals, including humans, and to provide methods for their production, including host cells capable of producing these proteins. Still another object is to provide antibodies capable of binding specifically to the proteins of this invention. Yet another object is to provide a biocompatible, in vivo biodegradable matrix capable, in combination with an osteoinductive protein, of producing endochondral bone formation in mammals, including humans.
These and other objects and features of the invention will be apparent from the description, drawings, and claims which follow.